1. Field of the Invention
This invention concerns a modified magnetron high-frequency discharge type plasma generation apparatus.
2. Description of the Related Art
In general, in order to fabricate a solid device, it is necessary to employ a surface treatment apparatus for subjecting the surface of the substrate of the solid device to some prescribed treatment. By solid device here is meant, for example, any semiconductor device or liquid crystal display device, etc. And by the substrate of the solid device is meant a substrate such as a wafer for a semiconductor device or glass plate for a liquid crystal display device.
Such surface treatment apparatuses include dry etching apparatuses and CVD (chemical vapor deposition) devices, and so on. By dry etching apparatus here is meant an apparatus for dry-etching the surface of a substrate. And by CVD apparatus is meant an apparatus for using a chemical reaction to form a prescribed thin film on the surface of a substrate.
Among these surface treatment apparatuses are plasma surface treatment apparatuses which use plasma to effect prescribed treatments on substrate surfaces. In order to implement such a plasma surface treatment apparatus, it is necessary to have a plasma generation apparatus for generating plasma.
In recent years, a demand has risen for plasma generation apparatuses which can generate plasma under conditions of low discharge gas pressure, reflecting the trend toward greater solid device miniaturization.
More specifically, when a solid device is further miniaturized, greater precision in the direction of ion incidence on the substrate is demanded. This incidence direction precision depends on the pressure of the discharge gas. That is, when the gas pressure is low, the incidence direction precision is higher, and when that pressure is high, the precision is lower. This is because, when the gas pressure is high, as the ions in the plasma impact the substrate while being accelerated by the sheath voltage on the surface of the substrate, they collide with neutral gas before reaching the surface. Thus it is necessary to generate plasma at low gas pressures to cope with further miniaturization in solid devices.
By low gas pressure, furthermore, although this will differ according to the type of surface treatment involved, is generally meant a pressure of 30 m Torr or less. By way of comparison, when a semiconductor device wafer is subjected to dry etching, the plasma should be generated with a gas pressure of about 10 m Torr.
The magnetron high-frequency discharge type of plasma generation apparatus has been known for some time as a plasma generation apparatus capable of generating plasma at low gas pressures. This apparatus generates plasma by magnetron discharges using a high-frequency electric field.
An example of such a plasma generation apparatus is described in the literature cited below.
Reference: Unexamined Patent Application [Tokkai] No. H7-201831 [1995].
The plasma generation apparatus described in the cited literature is fashioned so that it generates plasma by generating magnetron discharges by a high-frequency electric field formed by a cylindrical discharge electrode and a magnetic field formed by ring-shaped permanent magnets.
With the plasma generation apparatus described in the cited patent application, however, there is a problem in that high-density plasma cannot be generated in the center of the plasma generation region. This is due to fact that, in this plasma generation apparatus, plasma is mainly generated at the surface of the discharge electrode. By center of the plasma generation region here is meant the center in the radial dimension of the discharge electrode (and so hereinafter).
Thus, with this plasma generation apparatus, when a plasma surface-treatment apparatus is implemented, there is a problem in that surface treatment cannot be performed under uniform plasma density conditions.
In order to resolve this problem, it is only necessary to install the susceptor in a location that is considerably removed from the discharge electrode in the axial direction thereof. By susceptor here is meant a substrate carrier on which the substrates being processed are carried.
With such a configuration as this, however, although it is possible to perform surface treatment under uniform plasma density conditions, it is not possible to perform surface treatment under conditions of high plasma density, which constitutes a new problem. This is due to the fact that, in a plasma generation apparatus such as that described above, as the distance from the discharge electrode increases in the axial direction, plasma density declines due to plasma diffusion loss. As a consequence, with such a configuration as this, de surface treatment processing speed becomes slow.
In view of the foregoing, there is a need for a modified magnetron high-frequency type of plasma generation apparatus that can generate high-density plasma in the center of the discharge electrode as well as at the periphery. By periphery of the plasma generation apparatus here is meant the peripheral region in the radical dimension of the discharge electrode (and so hereinafter).
Thereupon, an object of the present invention is to provide a modified magnetron high-frequency discharge type plasma generation apparatus capable of generating high-density plasma in the center of the plasma generation region as well as at the periphery.
The plasma generation apparatus for the purpose of resolving the problem noted above, comprises a vacuum vessel, gas induction means, exhaust means, discharge electrode, first high-frequency electric power application means, magnetic force line formation means, and two walls.
The vacuum vessel is a vessel in the interior of which is established a plasma generation region. The gas induction means are means for inducting discharge gas into the interior of the vacuum vessel. The exhaust means are means for exhausting the atmosphere in the interior of the vacuum vessel. The discharge electrode is an electrode positioned so as to enclose the plasma generation region. This electrode is formed in a cylindrical shape.
The first high-frequency electric power application means are means for applying high-frequency electric power to the discharge electrode. The magnetic force line generation means are means for forming prescribed lines of magnetic force. These magnetic force lines have portions that roughly parallel the discharge electrode center axis, the length of these parallel portions becoming longer the closer they are to the center axis. The two walls are walls that define the scope of the plasma generation region in the dimension of the discharge electrode center axis. These two walls are positioned so as to sandwich the plasma generation region between them in the dimension of the center axis of the discharge electrode.
The plasma generation apparatus moreover, is characteristic in that it is configured so that the magnetic force lines that pass through the center of the plasma generation region are shaped so that they do not intersect the two walls.
These magnetic force lines are formed, for example, by suitably setting the size of the vacuum vessel, the position and configuration of the magnetic force lines forming means, and the position of and interval between the two walls, etc.
With the plasma generation apparatus when plasma is generated, discharge gas is inducted by the gas induction means into the interior of the vacuum vessel. When is done, furthermore, the atmosphere in the interior of the vacuum vessel is exhausted by the exhaust means. Thus the interior of the vacuum vessel is established in a condition of reduced pressure. In this case, moreover, high-frequency electric power is applied to the discharge electrode. Thus is formed a high-frequency electric field component oriented in the radical direction of the discharge electrode. And, furthermore, magnetic force lines having portions roughly parallel to the center axis of the discharge electrode are formed by the magnetic force lines forming means. Thus are formed a high-frequency electric field and magnetic field that are mutually perpendicular in the plasma generation region. As a consequence, the electrons emitted by the discharge electrode exhibit magnetron motion. This magnetron motion generates magnetron discharges. Plasma is generated by the magnetron discharges.
With this apparatus, configured in this way, the magnetic force lines that pass through the center of the plasma generation region are established having a shape wherewith they do not intersect the two walls. Thus the outflow of high-energy electrons can be suppressed in the center of the plasma generation region.
By high-energy electron outflow here is meant the flowing out, through the walls, of high-energy electrons trapped by the magnetic force lines. This outflow occurs irrespective of the material of which the two walls are made. That being so, this outflow is determined by the difference between the surface potential on the two walls and the plasma space potential, and by the positional relationship between the two walls and the magnetic force lines formed in the plasma generation region.
By means of this suppression, magnetron discharge generation efficiency can be enhanced in the center of the plasma generation region just as at the periphery. Thus plasma generation efficiency is enhanced in the center of the plasma generation region as at the periphery thereof. As a consequence, high-density plasma can be generated in the center of the plasma generation region just as in the periphery.
The plasma generation apparatus wherein the two walls are formed of a material exhibiting electrical conductivity.
With the plasma generation apparatus described above and the two walls are formed of a material exhibiting electrical conductivity, it is possible, using these walls, to electrically control the density of the plasma.
The plasma generation apparatus as described above further includes second high-frequency electric power application means for applying high-frequency electric power to one of the two walls.
With the plasma generation apparatus as described above, wherein high-frequency electric power is applied by the second high-frequency electric power application means to one of the two walls. Thus a high-frequency electric field is formed in the center axial dimension of the discharge electrode. As a consequence, the high-energy electrons trapped by the magnetic force lines exhibit high-frequency oscillation in the direction of the center axis of the discharge electrode. This high-frequency oscillation generates discharges (hereinafter called xe2x80x9chigh-frequency oscillation dischargesxe2x80x9d) that differ from the magnetron discharges. As a result, plasma generation efficiency is enhanced.
The high-frequency oscillation discharge generation efficiency rises higher in the center of the plasma generation region than at the periphery. This is so because, in the magnetic force lines, the portions thereof parallel to the discharge electrode center axis become longer the closer they are to the center axis. Thus plasma generation efficiency in the center of the plasma generation region is enhanced.
The plasma generation apparatus as described above, wherein the other of the two walls is connected to a reference potential point.
With the, plasma generation apparatus and the other two walls is connected to the reference potential point, the average plasma space potential can be made low. As a result, it is possible to reduce contamination by metal from the other electrode surface connected to the reference potential point.
The plasma generation as described above, wherein the other of the two walls is established in an electrically floating state.
With the plasma generation apparatus as described above, the other of the two walls is established in an electrically floating state. Thus it is possible to reduce the damage done in the other of the two walls by the sheath voltage. The plasma generation apparatus as described above, wherein the other of the two walls is use holder for holding the object being treated when that object being treated is subjected to a prescribed treatment.
With the plasma generation apparatus as described above, it is possible to lower the sheath voltage in the surface of the object being treated that is being held by the other of the two walls. Thus it is possible to reduce the damage done to the object being treated by the sheath voltage.
The plasma generation apparatus as described above, wherein the first-frequency electric power application means comprises a first high-frequency electric power supply for outputting the high-frequency electric power applied to the discharge electrode. Moreover, the second high-frequency electric power application means comprises a second high-frequency power supply for outputting the high-frequency electric power that is applied to one of the two walls by the second high-frequency electric power application means.
With the plasma generation apparatus as described above, the high-frequency electric power applied to the discharge electrode is output from the first high-frequency electric power supply. On the contrary, the high-frequency electric power applied to one of the two walls is output from the second high-frequency electric power supply. Thus the magnitude of the high-frequency electric power applied to the discharge electrode and the magnitude of the high-frequency electric power applied to one of the two walls can be set independently. As a consequence, the density of the plasma generated by the magnetron discharges and the density of the plasma generated by the high-frequency oscillation discharges can be set independently. Thus it is possible to establish the density distribution of the plasma in the radial dimension of the discharge electrode as a uniform density distribution.
The plasma generation apparatus as described above, wherein the first high-frequency electric power application means comprises high-frequency electric power supply for outputting the high-frequency electric power applied to the discharge electrode. In this apparatus, moreover, the second high-frequency electric power application means comprises a high-frequency resonant circuit that resonates with the high-frequency electric power output by the high-frequency electric power supply.
With the plasma generation apparatus, the high-frequency electric power applied to the discharge electrode is provided by the high-frequency electric power supply. On the contrary, the high-frequency electric power applied to one of the two walls is provided from the high-frequency power supply via the high-frequency resonant circuit. Thus the number of high-frequency electric power supplies can be limited to one. As a consequence, it is possible both to keep the apparatus circuit configuration simple and to reduce manufacturing costs.
The plasma generation apparatus as described above both of the two walls are connected to the reference potential point.
In the plasma generation apparatus described both of the two walls are connected to the reference potential point. This makes it possible to lower the average plasma apace potential even further. As a result, contamination by metal from the surface of the electrode connected to the reference potential point can be suppressed to a bare minimum. The plasma generation apparatus as described above, further includes control means for controlling the magnitude of the high-frequency electric power applied by the first high-frequency electric power application means to the discharge electrode.
With the plasma generation apparatus as described above the magnitude of the high-frequency electric power applied to the discharge electrode is controlled by the control means. Thus the density of the plasma generated by the magnetron discharges can be controlled.
The plasma generation apparatus as described above, further includes control means for controlling the high-frequency electric power output by the first and second high-frequency electric power supplies.
With the plasma generation apparatus as described above the magnitude of the high-frequency electric power applied to the discharge electrode and the magnitude of the high-frequency electric power applied to one of the two wails are controlled by the control means. Thus the density of the plasma generated by the magnetron discharges and the density of the plasma generated by the high-frequency oscillation discharges can be controlled. An a consequence, the density distribution of the plasma in the radial dimension of the discharge electrode can be controlled. The plasma generation apparatus as described above, wherein the control means are configured so that, when controlling the magnitudes of the high-frequency electric power output by the first and second high-frequency electric power supplies, both magnitudes are controlled such that the ratio between them is always a predetermined value.
With the plasma generation apparatus as described above the magnitudes of the high-frequency electric power output from the first and second high-frequency electric power supplies are continually controlled so that the ratio between the two magnitudes is a predetermined value. Thus, when controlling the plasma density, that control can be effected while continually maintaining the prescribed plasma density distribution in the radial dimension of the discharge electrode. Also, by designating the magnitude of the high-frequency electric power output from either one of the first and second high-frequency electric power supplies, the magnitude of the high-frequency electric power output from the other is automatically corrected. Thus the operator work load when controlling the magnitude of the high-frequency electric power can be reduced. The plasma generation apparatus as described above, further comprising control means for controlling the magnitude of the high-frequency electric power output by the high-frequency power supply.
With the plasma generation apparatus as described above by controlling the magnitude of the high-frequency electric power output by the high-frequency electric power supply, the magnitude of the high-frequency electric power applied to the discharge electrode is controlled. At the same time, furthermore, the magnitude of the high-frequency electric power applied to one of the two walls is also controlled. Thus the operator work load when controlling the magnitude of the high-frequency electric power can be reduced. The plasma generation apparatus as described above, further includes position adjustment means for adjusting the positions of the two walls in the center axial dimension of the discharge electrode.
With the plasma generation apparatus as described above the positions of the two walls in the center axial dimension of the discharge electrode can be adjusted. Thus, after the apparatus has been assembled, magnetic force lines can be formed that do not intersect the two walls. As a consequence, the formation of such magnetic force lines is made easy.
The plasma generation apparatus as described above, wherein one of the two walls is used as a gas diffusion plate for diffusing the discharge gas in the plasma generation region. In this apparatus, furthermore, the other of the two walls is used as a holder for holding the object being treated when subjecting that object being treated to a prescribed treatment using the plasma.
With the plasma generation apparatus as described above the discharge gas inducted by the gas induction means is dispersed in the plasma generation region by one of the two walls. Thus the discharge gas is supplied uniformly throughout the plasma generation region. With this apparatus, furthermore, when the plasma is used to perform a prescribed treatment on an object being treated, that object being treated is held by the other of the two walls. Thus a plasma treatment apparatus can easily be configured from the plasma generation apparatus.
The plasma generation apparatus as described above, includes a vacuum vessel, gas induction means, exhaust means, discharge electrode, first high-frequency electric power application means, magnetic force line formation means, two walls, and second high-frequency electric power application means.
Here the vacuum vessel is a vessel having a plasma generation region established in its interior. The gas induction means are means for inducting the discharge gas into the interior of the vacuum vessel. The exhaust means are means for exhausting the atmosphere in the interior of the vacuum vessel. The discharge electrode is an electrode deployed so as to enclose the plasma generation region. This electrode is formed in a cylindrical shape. The first high-frequency electric power application means are means for applying high-frequency electric power to the discharge electrode. The magnetic force line formation means are means for forming magnetic force lines in the plasma generation region. The two walls are walls that define the scope of the plasma generation region in the center axial dimension of the discharge electrode. These two walls are formed of a material exhibiting electrical conductivity, and are deployed so as to sandwich the plasma generation region between them in the center axial dimension of the discharge electrode. The second high-frequency electric power application means are means for applying high-frequency electric power to one of the two walls.
With the plasma generation apparatus as described above when generating plasma, discharge gas is inducted into the interior of the vacuum vessel by the gas induction means. When this is done, the atmosphere in the interior of the vacuum vessel is exhausted by the exhaust means. Thus the interior of the vacuum vessel is established in a reduced pressure state. When this is done, moreover, high-frequency electric power is applied to the discharge electrode. Thus a high-frequency field is formed that is oriented in the radial direction of the discharge electrode. In addition, when this is so, magnetic force lines are formed in the plasma generation region by the magnetic force line formation means. Thus the electrons exhibit magnetron motion. As a result of this magnetron motion, magnetron discharges are generated. As a result of these magnetron discharges, plasma is generated.
In this case, high-frequency electric power is supplied to one of the two walls. As a result, a high-frequency electric field is formed facing in the center axial direction of the discharge electrode. As a consequence, high-energy electrons trapped by the magnetic force lines exhibit high-frequency oscillation. As a result, discharges are generated that differ from the magnetron discharges. As a consequence, plasma generation efficiency can be raised higher than it can be with magnetron discharges only.
Comprehended in this apparatus, moreover, are cases wherein there are no magnetic force lines which do not intersect with the two walls. In such cases, the number of high-energy electrons trapped in the magnetic force lines becomes small. As a result, the efficiency of plasma generation by magnetron discharge deteriorates. With this apparatus, however, high-frequency oscillation discharges are obtained. As a result, the decline in the efficiency of plasma generation by magnetron discharge is compensated for.